1. Field of the Invention
Aspects of the present invention relate to a cathode comprising an active material composite and to a lithium battery using the same, and more particularly, to a cathode comprising an active material composite that can improve electrode performance by improving the conductivity characteristics during initial charging/discharging cycles, and to a lithium battery using the same.
2. Description of the Related Art
In general, transition metal compounds such as LiNiO2, LiCoO2, LiMn2O4, LiFePO4, LiNixCo1−xO2(0<x<1) and LiNiyMnyCo1−2yO2(0<y<0.5), and oxides of these compounds and of lithium are widely used as cathode active materials for lithium batteries. Recently, various composite oxides have been proposed as alternatives to address the ever increasing demand for higher capacity batteries.
One such composite oxide, xLi2MO3-(1−x)LiMeO2, is a solid-solution complex of Li2MO3 and LiMeO2 where M is a group of metal elements including at least one of Mn, Zr, and Ti, and Me is a group of metal elements including at least one of Ni, Co, Mn, Cr, Fe, V, Al, Mg, and Ti. The complex, which is a solid-solution, has a layered structure, with respective layers of Li2MO3 and LiMeO2, where excess lithium is substituted in a transition metal layer.
For example, in the case of the solid-solution complex component, Li2MO3, where manganese (Mn) is used as the transition metal M, Mn has an oxidation number of +4 during the charge cycle but the oxidation number of Mn in the oxygen layer is between +4 or +5, thus not permitting Mn to contribute to electric conductivity. In addition, if a battery has a capacity high enough to be feasible, lithium accounts for approximately 10 to 20 atomic percent of the composition of the transition metal layer. Because of the excess of lithium, Mn predominates at more than two times the content of lithium. Thus, the proportion of transition metals actually contributing to electric conductivity, e.g., Ni, Co, or the like, is restricted, resulting in a reduction in the electric conductivity of the cathode active material. Accordingly, in order to effectively utilize the xLi2MO3-(1−x)LiMeO2 complex as a cathode active material, a need exists to solve the problem associated with electric conductivity of the complex.